The present invention relates generally to a data error detecting apparatus for a key telephone system and the detecting method therefor, and more specifically to an apparatus and a method of detecting data errors generated in a key telephone system connectable to an Integrated Service Digital Network (referred to as ISDN, hereinafter).
With the development of the ISDN recently, an ISDN interface unit is usually provided in a key service unit of a key telephone system for connection between the ISDN and the key telephone system. The above-mentioned ISDN interface unit transmits digitalized speech signals or data signals given through a telephone office line (i.e. digital outside line), without conversion into analog signals, to the key service unit, to which a plurality of terminal devices (e.g. key telephone sets) are connected. In addition, the ISDN interface unit can transmit digitalized speech signals or data signals given from the terminal devices through the key service unit to the office line without conversion into analog signals.
In case an error is detected in the data transmitted to the key service unit, a test (referred to as a loop-back test) is made for each transmission line in the system, in order to locate the position at which the data error occurs within the key service unit and peripheral devices thereof, as described in further detail below. In the loop-back test, a tester (referred to as a loop-back tester) is first connected to a location to be tested of the key service unit; secondly, random data (e.g. 511 random pattern data) is transmitted from the loop-back tester to the test location; the random data transmitted to the test location is compared with that returned from the test location by the loop-back tester; and the occurrence of data error at the test location is detected when the data do not match with each other.
In the conventional data error detecting method, however, the locations to be loop-back tested are limited to locations to which the loop-back tester can be connected from the outside of the key service unit, for instance such as terminals of the ISDN interface unit. In more detail, when the loop-back tester is connected to a terminal of the ISDN interface unit from the outside of the key service unit, it is possible to detect the occurrence of data error generated in a transmission line between the loop-back tester and a return point in the ISDN interface unit (from which a test data transmitted from the tester is returned). In the conventional test method, however, there exists a problem in that it is impossible to detect the occurrence of data error generated due to trouble at locations other than the ISDN interface unit within the key service unit, for instance such as an up-stream speech highway, a down-stream speech highway, etc. In addition, whenever the conventional loop-back test is made, since it has been necessary to stop the service or operation of the key telephone system, there exists another problem in that it is impossible to perform the loop-back test at any time when required.